Electrolytic recovery of zinc from ores and other zinc-bearing materials.



E TA PAW @E.

URLYN CLIFTON TAINTON, F JOHANNESBURG, TRANSVAAL, SOUTH AFRICA.

ELECTROLYTIC RECOVERY OF ZINC FROM ORES AND OTHER ZINC-BEARDHG MATERIALS.

No Drawing.

ber 1,059,233, dated th April, 1913, granted to the present applicant and John Norman Pring jointly, a process is described for extracting zinc by electrolysis from a solution or electrolyte of a specified constitution or composition. According to said specification the requisite solution is obtained by taking or forming a solution of a salt of zinc (for j example zinc sulfate) and adding thereto a large proportion of acid (for example sulfuric acid) and a small proportion of a colloid agent (for example gum tragacanth),

The deposition of the metallic zinc out of said solution is effected by electrolyzing such solution with a current of high density. The present application appertains to a continuous or cycli c process for the production of such solution directly from ores or other zinc-bearing materials, and to the use of said solution in the aforementioned process for recovering zinc electrolytically.

A feature of the present process is that it can be carried out Without loss of acid or accumulation of impurities.

According to the present invention, in a process for the electrolytic extraction of metallic zinc from its ores or other zinc-bearing material, the solution is regenerated by dividing it into two portions, treating fresh ore with one portion thereof to dissolve zinc and neutralize its acid content, and there after mixing the neutral solution with the remaining portion for further treatment by electrolysis with a current of high density (for example 50-1000 amperes per square foot) the proportion employed for treating the fresh ore preferably being such that on neutralizing the. said content with fresh ore and mixing the resulting neutral solution with the remaining solution, the mixture contains from 530% of free acid. The proc ess may often be carried out without the ad- Application filed August 10, 1915.

Specification of Letters Patent. Patented Dec. 28, E916.

Serial No. 44,837.

dition of any colloid, since colloidal silica is usually produced in the solutionsby the action of the acid on the ores from which they are formed. A colloid may, however, be added if desired. V

One method of carrying out this invention will now be described. The ore or other material from which the zinc is to be ex- 7 ore is then treated with an acid, as for example sulfuric acid. This may be efiected -by percolation, leaching, or agitation, the

last method, which is ordinarily applicable, being preferred, as it shortens the time of such treatment. The acid is added in quantity just sufiicient to take up the zinc in the ore and leave a neutral solution. This solution is then, if necessary, separated from suspended solid matter, by filtration or settlement, and then acidified by means of a further quantity of acid. When the solu tion has been separated from the treated ore, the latter is Washed with water which is then added to the solution. It is desirable to filter the solution while hot to prevent the zinc sulfate from crystallizing out during filtration. It is preferable so to arrange that the concentration of both zinc and acid in the solution contains a fairly high value, as for example 140 (one hundred and forty) grams of zinc per liter and from 50-300 (fifty to 150 (one hundred and fifty) to 170 (one.-

hundred and seventy) grams of sulfur c acid per liter.-

The solution is then regenerated from the ore in the following way: The solution is divided into two portions such that one portion contains as much free acid as the whole of the original solution did before the electrolysis. This statement may be explainedby taking an example. Assuming that the original content of the solution was (seventy-five) grams per liter of free acid and the final content was 150 (one hundred and fifty) grams per liter and the total volume of solution remained the same, then one half of the final solution would be taken. This portion is then kept separate and the remaining portion is used for dissolving out the zinc from a fresh charge of ore. The quantity of ore used is such as will just neutralize all the acid in the portion of the electrolyzed solution taken. When neutralization is practically complete a small quantity of fresh ore is added in order to complete the neutralization and precipitate iron. The solution is then separated from the residue and added-to the strongly acid solution which has been retained in the storage vat. When the solution has been separated from the treated ore, the latter is washed with water which is then added to the solution. The acid content of the mixed solution is thereby brought back to its original concentration. The solution may be then again electrolyzed and the operation repeated. Though the presence of iron in the solution does not adversely affect the physical character of the zinc deposited therefrom yet in treating ores for the extraction of zinc by the cyclic process according to the present invention, the iron dissolved in the ore will, if it is not eliminated, gradually increase until it eventually attains a high concentration in the electrolyte and thereby leads to the contamination of the deposited zinc and also tends to lessen the efliciency of the process when the electrolysis is long continued. It is advisable therefore in the present process to precipitate the iron from the solution by the addition of fresh ore.

The quality of the metal deposited under these conditions is very good, and it may be used directly 'as a galvanizing coating for the protection of iron against corrosion. If, however, the zinc is required in the form of solid metal the cathode used may be of such a nature that the de os'it of zinc is readily detached from it, as or example, aluminium,

-or oiled 0r graphite-covered copper. The

zinc after being detached may be then melted up and cast. Alternatively the zinc may be deposited on thin sheets of zinc foil, which may be then melted without strippin or a cathode of iron or other material 0 hi h fusin point may be used, in which case t e zinc eposit may be removed by dippin said cathode in a bath of molten zmc,'fu zincchlorid, et cetera, and the cathode thenreturned to the depositing vat. If the amount of sulfuric acid consumed by the ore is in excess of that theoretically required, it is which accrue from the use of a high current density, high acid content and the presence of a colloid (wide the specification of our prior patent) whereby such solution can be prepared direct from ores and other impure materials without loss of acid or accumulation of impurities.

(b) It is possible to extract metallic zinc directly from the ore, and to 'deposit such zinc immediately in a form in which it may be used as a protective coating for iron or steel in one operation. This has not been desirable to arrange the roasting so that a possible on a commercial scale according to known recesses.

(0) 11 account of the high acid content of the solution used for dissolving out the zinc in the ore, the zinc is very rapidly dissolved, and the plant necessary for this operation can be relatively very small; and on account of the high current densities used in the electro-deposition, the depositing plant required is also relatively small, and the number of electrodes, et cetera, required very few.

(d) Under the conditions described itis possible to extract a large amount of. zinc from the solution without regeneration of the solution. In this connection it may be stated that this has been one of themain difficulties in the past, as the current efficiency of the zinc electrolysis fell ofl rapidly as the acid content rose. For this reason, therefore, it was possible to continue the electrolysis only by the provision of s ecial means to prevent the accumulationo acid in the solution, for example, diaphragms,

soluble anodes, et cetera. With the solution (e) In the case of ores containing iron and manganese, by the neutralization of the solution, and subsequent addition of a small quantity of ore, all iron present may be precipitated. Manganese also, which has proved an insuperable obstacle in the past,

owing to the formation of permanganic acid and consequent resolution of the zmc, 1s continuously eliminated during electrolysis, as I have found that under the conditions described manganese is continuously precipitated at the anodes as manganese dioxid, and can be readily removed from the solution by filtration orsettlement. The accumulation of manganese salts in the solution is thereby prevented, and the presence of manganese in an ore exerts, therefore, no deleterious eflect whatever upon the quality of the deposits obtained.

(f) Inthe case of many ores it is possible to vary the quality of the deposits, by making'use of the silicic acid formed by the action of the acid solution on the silicates in the ore. This can be used to take the place of the colloid which, as described in the specification of the previous patent, is necessary for the formation of lustrous deposits of zinc.

(g) As the residues are extracted from the solution when neutral, there is no deleteri- Qous acid effect on pumps, filters and other plants necessary for handling the solution.

The solution prepared according to the present invention, that is, one having a high acid content would be practically useless in any process known in the art except that described in the prior application for patent hereinbefore mentioned as it has not hitherto been possible under ordinary practice to recover metallic zinc from a solution containing a high percentage of free acid and containing also other metals electronegative to zinc.

What I claim as my invention and desire to protect by Letters Patent is? 1 A continuous electrolytic process for the extraction of zinc from a zinc-bearing material which consists in forming therefrom a concentrated solution of a zinc-salt containing an excess of acid, electrolyzing the solution with a current of high density, regenerating the said solution by dividing itinto two portions in such proportions that, when the acid in one portion is neutralized by the addition to it of a charge of zinc-bearing material and the resulting solution separated from the residue and mixed with the other portion of the electrolyzed solution which has been retained, the acid-contentfof the final solution shall be approximately the same as that of the original solution, and then electrolyzing the regenerated solution with a current of high density. v

2. A continuous process for the electroly tic extraction of metallic zinc from a zincbearing material, which consists in adding sufficient of the zinc-bearing material to an acid to make a neutral solution,- separating the neutral solution from the residue, adding an excess of acid and a small proportion of a colloid, electrolyzing said solution by means of a current of high density and thus removing part of the zinc; then removing the solution now strongly acid and dividing it into two portions, neutralizing one portion by a further addition of zinc-bearing material, separating the neutral solution from the residue, adding'the other portion of the removed solution and electrolyzing the acid solution so formed; and thereafter repeating the regenerating and electrolyzing'process as described.

3. A continuous process for the electrolytic extraction of metallic zinc from a zincbearing material which consists in adding sufficient of the zinc-bearing material to an acid to, make a neutral solution, separating the neutral solution from the residue, adding an excess of acid, and electrolyzing said solution by means of a current of high density and thus removing part of the zinc; then removing the solution now strongly acid and dividing it into two portions, neu- .lytic extraction of metallic zinc from a zinc-bearing material, which consists in adding suflicient of the zinc-bearing material to an acid to make a neutral solution containing the colloid required in the production of smooth zinc deposits, separating the neutral solution from the residue, adding an excess of acid, and electrolyzing said solution by means of a current of high density and thus removing part of the zinc; then removing the solution now strongly acid and dividing it into two portions, neutralizing one portion by a further addition of zinc-bearing material, separating the neutral solution from the residue, adding the other portion of the removed solution, and electrolyzing the acid solution so formed; and thereafter repeating the regenerating and electrolyzing process as described.

the extraction of zinc from its ores which consists in forming therefrom a concentrated solution of a zincsalt containing from 50300 grams of free acid per liter, electrolyzing the solution with a current of high density, regenerating the said solution by dividing it into two parts in such proportions that, when the acid in one portion is neutralized by the addition to it of a' charge of ore and the resulting solution separated from the residue and mixed with the other portion of the neutralized solution which has been retained, the acid content of the final solution shall be approm'- &

mately the same as that of the original solution, and then electrolyzing the regenerated solution with a current of high density.

' 6. A continuous process for the electrolytic extraction of zinc from its ores which consists in adding sufiicient of the ore to an acid to make a neutral solution, separating the neutral solution from the residue, adding an excess of from 50-300 grams of free acid per liter and a small proportion of a colloid, electrol zing said solution by means of a current of iiigh density and thus removing part of thezinc; then removing the solution now strongly acid and dividing it into two portions, neutralizing one 'portion by a further addition of ore, separating the neutral solution from the residue, adding the other portion of the removed solution, and electrolyzing the acid solution so formed; and thereafter repeating the regenerating and electrolyzing process as described.

\ 7 A continuous process for the electrolytic extraction of metallic zinc from'its ores which consists in adding suflicient of the ore to an acid to make a neutral solution, separating the neutral solution from the residue, adding an excess of from 50-300 grams of free acid per liter, and electrolyzing said solution by means of a current of high density and thus removing part of the zinc; then removing the solution now strongly acid and dividing it into two portions, neutralizing one portion by a further addition of ore, adding a slight excess of ore to the neutral solution to remove any iron or other impurities present, separating the neutral solution from the residue, adding the other portion of the removed solution, and electrolyzing the acid solution so formed; and thereafter repeating the regenerating and electrolyzing process as de scribed.

8. A continuous process for the electrolytic extraction of metallic zinc from its ores which consists in adding suflicient of the oreto an acid to ing the neutral solution from the residue, adding an excess of from 50-300 grams of free acid per liter and electrolyzing said solution bymeans of and thus removing part of the zinc; then removing the solution now strongly acid and dividing it into two portions, neutralizing one portion by a further addition of ore,

separating the neutral solution from the residue, adding the other portion of the removed solution and electrolyzing the acid solution so formed; and thereafter repeating the regenerating and electrolyzing process as described.

-9. In a continuous electrolytic process for the extraction of zinc from a zinc-bearing material in which a solution of a zinc salt containing an excess of acid is electrolyzed.

with a current of high density, the step of regenerating the solution by dividing the.

same into two port-ions in such proportions that when the acid in one portion is neuseparata current of high density make a neutral solutlon containing the colloid required in the production of smooth zinc deposits,

tralized by the additionthereto of a charge of zinc-bearing material and the resulting solution separated from the residue and mixed with the other portion of said electrolyzed solution which has been retained, the acid-content of the final solution is approximately the same as that of the original solution. y

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

URLYN CLIFTON TAINTON. Witnesses:

ARTHUR THOMPSON, VIOLET WELLS. 

